1. Field of the invention.
The present invention relates to pipelines and more particularly to minimizing oxidation of pipelines under a roadbed.
2. Description of the prior art.
It has been common practice to surround that portion of a pipeline, extending transversely of a roadbed beneath the soil, with a length of loosely surrounding casing to minimize oxidation of the line. Further, the respective ends of the casing are preferably sealed with the perimeter of the pipeline to prevent moisture contacting the pipeline within the surrounding casing. The casing is usually vented to the atmosphere at opposite sides of the road so that, in the event of a pipeline rupture under the roadbed, any fluids would be safely discharged laterally of the road.
With proper seals interposed between the inner periphery of the casing and the periphery of the pipeline, which electrically isolates the pipe line from the road crossing casing, an inert gas can be injected through one of the vents with the vents provided with closeable valves. With the gas under greater than atmospheric pressure substantially all corrosive action on the perimeter of the pipeline is eliminated.
This invention provides access valves and low pressure vent relief valves to accomplish this purpose.